The present invention relates to an artificial vessel which has a stress-strain curve and a compliance approximate to those of a vital vessel, and has pores throughout the thickness of the vessel wall, and relates to a process for preparation of the same.
In recent days, investigation on an artificial vessel has proceeded and many artificial vessels have been developed with the progress of vascular surgery. At present, examples of the clinically used artificial vessels for arteries with a large diameter of not less than 6 mm are, for instance, the DeBakey artificial vessel made of woven Dacron (USCI. Co., Ltd. of U.S.A.), and Gore-Tex (Gore. Co., Ltd. U.S.A.) which is made of an expanded potytetrafluorethylene (hereinafter refered to as "EPTFE").
Those conventional artificial vessels have pores which communicate between the inside of the vessel and the outside the vessel. When the vessel is grafted into a living body, the outside of the vessel is covered with pseudointima and the pseudointima grows into the communicating pores to cover the inside of the vessel, i.e., the vessel is organized, which prevents the formation of thrombus or occlusion by thrombus and thus makes the artificial vessel stable in the living body. The property whereby the communicating pores serve to make the artificial vessel organize is referred to as "porosity".
The compliances of such conventional artificial vessels are very different from those of vital vessels, which causes various problems due to compliance mismatch such as anastomotic punnus hyperplasia long after the grafting in a living body. Particularly, the conventional artificial vessels cannot be clinically used as an artificial artery with a small diameter of not more than 6 mm because the compliance mismatch remarkably increases to make patency of the vessel poor. Therefore self-veins are used for vascular reconstructive surgery of coronary arteries or arteries below the knees.
For the above reason, in development of artificial vessels, particularly artificial arteries with a small diameter, it is important that the compliances of artificial vessels are matched with those of vital vessels, in addition the artificial vessels having a porosity and the blood compatibility of artificial vessels being improved.
According to the report by Sasajima et al, J. Artif. Organs 12(1), 179-182(1983), however, the compliance of the practically available artificial vessels is much smaller than those of vital vessels, as shown in Table 1. As is clear from Table 1, the practically available artificial vessels are very hard to comparison with vital arteries, in other words, the artificial vessel is like a rigid vessel.
TABLE 1 ______________________________________ Vessel Compliance ______________________________________ Thoracic aorta of dog 0.749 Abdominal aorta of dog 0.491 Carotid artery of dog 0.356 Double Velour Dacron 0.058 Woven Dacron 0.021 EPTFE 0.028 ______________________________________
In order to solve such compliance mismatch, a process for preparing an artificial vessel of an elastomer which has a porous wall and a compliance approximate to that of a vital vessel is disclosed in U.S. Pat. No. 4,173,689. The artificial vessel prepared according to the process does not have porosity. Further, the artificial vessel has very small pores on its wall and a relatively dense structure. Although the compliance of the artificial vessel prepared according to the process disclosed in the U.S. Patent is surely larger than that of the conventional artificial vessel, the compliance is still smaller than that of a vital vessel and is not sufficient.
For preparing an artificial vessel approximate to a vital vessel, it should be attempted to match the stress-strain curve of an artificial vessel with that of a vital vessel. The typical stress-strain curve of one of the prior artificial vessels is curve I in FIG. 4, and stress-strain curves of vital vessels are curves III and IV in FIG. 4. As is clear from FIG. 4, when a high blood pressure beyond normal blood pressure range is applied to those vessels, the stress-strain curve I of the prior artificial vessel shows different behaviour from those of the curves III and IV of the vital vessels. Accordingly, the prior artificial vessels have possibilities of breakage and damage when an abnormal blood pressure is applied, for instance, in a surgical operation, and also have insufficient durability.
An object of the present invention is to provide an artificial vessel having a porosity, and also having a compliance and a stress-strain curve approximate to those of a vital vessel.
Another object of the invention is to provide a process for preparing such an artificial vessel.
These and other objects of the invention will become apparent from the description hereinbelow.